The present invention relates to a method of predicting the bending life of wires, which are formed by coating conductor wires with insulating layers, supplying electric signals of an automobile and an industrial apparatus and electric-electronic apparatuses mounted thereon and power from a power source or a wire harness (wire harness) thereof up to disconnection caused by bending.
As is well known, a large number of wires are used for an automobile or an industrial apparatus. Among the wires or a wire harness prepared by bundling a plurality of wires (the wires and the wire harness are hereinafter generically referred to as xe2x80x9cwire or the likexe2x80x9d), there is a one arranged on a position such as a door portion or a seat portion of an automobile subjected to bending, for example, and such a wire or the like may lead to disconnection when repetitively subjected to bending deformation.
Therefore, it is important to evaluate bendability of the wire or the like, and a certain degree of bending life (the count of bending of the wire or the like leading to disconnection caused by bending) has been experimentally predicted from the degree of bending or the like in general. Particularly when the bendability has been regarded as important, the bending life has been evaluated by making a test in practice every time product conditions have been changed.
However, correct and objective evaluation cannot be performed when experimentally predicting the bending life, while it follows that a great deal of cost and time are required for designing the wire harness when making a test in practice every time the product conditions are changed.
Therefore, development of a method of predicting the bending life of a wire or the like on the basis of a theoretical basis is desired, and a technique disclosed in Japanese Patent Application Laid-Open No. 8-166333, for example, has been proposed. According to such a technique, the bending life is predicted on the basis of the maximum distortion quantity of a conductor part of a wire. However, it is only a single feeder such as a flat wire that allows calculation of the maximum distortion quantity, and this cannot be applied to a general wire (wire formed by stranding a conductor part).
The present invention has been proposed in consideration of the aforementioned subject, and the object thereof is to provide the bending life prediction method for a wire or a wire harness which can correctly predict its bending life regardless of product conditions of the wire or the like.
The present invention is a bending life prediction method for a wire for predicting the bending life of a wire, formed by coating a conductor wire with an insulating layer, up to disconnection caused by bending, which comprises a step of repetitively bending a wire (1) for previously obtaining correlation between its distortional change quantity and an actually measured value of the bending life, a step of calculating a distortional change quantity (xcex94xcex5) of the wire (1) serving as the prediction object, and a step of predicting the bending life of the prediction object wire by collating the said distortional change quantity (xcex94xcex5) of the prediction object wire as calculated with the said correlation.
Or, it is a bending life prediction method for a wire harness for predicting the bending life of a wire harness (2), prepared by bundling a plurality of wires formed by coating conductor wires with insulating layers, up to disconnection caused by bending, which comprises a step of repetitively bending the wires forming the said wire harness (2) for previously obtaining correlation between its distortional change quantity and an actually measured value of the bending life, a step of calculating a distortional change quantity (xcex94xcex5) of the wire harness (2) serving as the prediction object, and a step of predicting the bending life of the prediction object wire harness by collating the said distortional change quantity (xcex94xcex5) of the prediction object wire harness as calculated with the said correlation.
Desirably, the step of obtaining the said correlation obtains the said correlation by repetitively bending the said wire as to a plurality of distortional change quantities (xcex94xcex5) and actually measuring the count of bending up to disconnection.
Desirably, the step of obtaining the said correlation obtains the said correlation by executing the said measurement every temperature.
When predicting the bending life of the said wire (1) at this point, the said distortional change quantity (xcex94xcex5) is calculated by the following equation in the step of calculating the said distortional change quantity (xcex94xcex5) of the prediction object wire serving as the prediction object on the assumption that r represents the radius of the said wire (1), R1 represents the bend radius of the said wire (1) in a state most bent on a position bent/changed at the maximum within a region of the said wire (1) subjected to bending and R2 represents the bend radius of the said wire (1) in a most elongated state:
xcex94xcex5=rxc2x7(1/R1xe2x88x921/R2)
Thus, the bending life of the prediction object wire is predicted by repetitively bending the wire for previously obtaining the correlation between its distortional change quantity and the actually measured value of the bending life and thereafter calculating the distortional change quantity of the wire serving as the prediction object and collating the calculated distortional change quantity of the prediction object wire with the aforementioned correlation, whereby the bending life can be correctly predicted regardless of the product conditions of the wire.
Or, when predicting the bending life of the wire harness (2), the step of obtaining the said correlation obtains the said correlation as to a single wire by repetitively bending the said wire as to a plurality of distortional change quantities (xcex94xcex5) and actually measuring the count of bending up to disconnection, for calculating the said distortional change quantity (xcex94xcex5) by the following equation in the step of calculating the said distortional change quantity (xcex94xcex5) of the said wire harness (2) serving as the prediction object by supposing a single virtual wire member formed by weighted-averaging the said conductor wires and the said insulating layers by a sectional area ratio, regarding the virtual wire member as single said wire and assuming that r represents the radius of the said virtual wire member, R1 represents the bend radius of the said virtual wire member in a state most bent on a position bent/changed at the maximum within a region of the said virtual wire member subjected to bending and R2 represents the bend radius of the said virtual wire member in a most elongated state:
xcex94xcex5=rxc2x7(1/R1xe2x88x921/R2)
Thus, the bending life of the prediction object wire harness is predicted by repetitively bending a single wire forming the wire harness for previously obtaining correlation between its distortional change quantity and the actually measured value of the bending life and thereafter collating the calculated distortional change quantity of the prediction object wire harness with the aforementioned correlation, whereby the bending life can be correctly predicted regardless of product conditions of the wire harness.
Other objects and features of the present invention are clarified in the following description.